1. Field of the Invention
The invention relates in general to a level shifting circuit, and more particularly to an output voltage signal whose level is lower than a grounding level by using capacitor coupling effect.
2. Description of the Related Art
Nowadays, the level shifting circuit, which had been maturely developed, is widely used in various circuit applications. Referring to FIG. 1A and FIG. 1B, circuit diagrams of a level boosting shifter and a level stepping-down shifter of a conventional level shifting circuit are respectively shown. For example, the level boosting shifter 1 includes two groups of inverters A and B and transistors T1 and T2. The transistors T1 and T2 respectively provides a high voltage level HV for the inverters A and inverter B in response to the output signal So and the output-inverse signal SoB.
The inverters A and B respectively are controlled by the input signal Si and the input-inversed signal SiB to provide an output signal SoB and an output-inverse signal So, wherein the levels of the input signal Si and the input-inversed signal SiB are switched between a high reference level Vdd and a low reference level Vg, the levels of the output signal SoB and the output-inverse signal So are switched between high voltage level signal HV and the low reference level Vg, and the level of the high voltage level signal HV is higher than the high reference level Vdd. Thus, the level shifter 1 may generate the output signal So with level ranges between the high voltage level HV and the low reference level Vg according to the input signal Si with level ranges between the high reference level Vdd and the low reference level Vg.
The level stepping-down shifter 1′, which steps down the level of the signal, generates an output signal So with level ranges between the high voltage level HV and the low voltage level LV according to the output signal So and the output-inverse signal So′. In other words, the conventional level shifting circuit which simultaneously boosts the high signal level (equivalent to the high reference level Vdd) of the input signal Si to the high voltage level HV and steps down the low signal level (equivalent to the low reference level Vg) of the input signal Si to the low voltage level LV is implemented by two stages respectively including a level boosting shifter 1 and a level stepping-down shifter 1′ each having six transistors. Therefore, the conventional shift register will be more costive.